In composite construction of Road bridges, the main girders are placed along traffic direction at spacing of around 2.5 m to cover the deck width. Each girder is designed to take live loads passing in that alignment. Construction depth plays an important role in the design of the bridge and cost of approach. The depth of construction (top of road level to bottom of girder) is 2 m to 3.5 m for spans of 24 m to 45 m. Half through steel girders are constructed and it can be adopted for shorter spans due to its lesser moment of inertia.
In multi girder system, the each girder is designed to take loads in that strip. The depth of construction (bottom of main girder to road level) is high. Weight of steel used is high. Bracing and diaphragm arrangements add to weight and increase construction time. The construction is to be done in situ. Trestle beams and multiple columns are needed to support the deck. Elaborate formworks are needed. The crossing needs to be closed interfering traffic, which is not suitable for fast track construction. Ladder deck system steel usage is less but depth of construction is more, which leads to increase in the approach cost. More area exposed makes it vulnerable for rain and weathering agents. Half through steel construction main girder steel property alone is used. More depth of girder and quantum of steel are required, which is adoptable for short spans. More area exposed makes it vulnerable for rain and weathering agents. PSC U girder is used only for single lane Railway bridges. The casting is done at site needing elaborate form work, which is constructed for short spans up to 18 m and also not suitable for multi lane Road/Railway bridges.
Multi girder composite girder road over bridges with girder spacing around 2.5 m are constructed. Twin Girder ladder decks are constructed with cross girders at top flange level. Half through steel girders are being constructed, where main girder steel property alone is used. U shaped PSC girders are constructed for single lane Railway bridges for short spans. U shaped RCC girder and steel girder composite bridge has been constructed at Loco Works Railway station near Chennai for single lane road with main I girders of symmetrical sections flat bottom and top cross girders. The web of U girder is broken due to symmetrical flange of main girder. The top flange width of concrete is unequal and composite properties of the main girders are not fully used.
One of the prior art KR101654657, discloses a bridge construction method using the side beam and the slab segments. The through bridge comprises: the two or more side beams arranged at intervals in the transverse direction, wherein the bottom of an end is supported on the upper surface of both abutment units spaced from each other in the longitudinal direction forming a lower foundation; both end flanges directly supported on the upper surface of the side beam; and a U-shaped slab segment including a U-shaped floor board unit formed between the both end flanges, wherein the U-shaped floor board unit is in contact with the inner surface of the side beams adjacent to each other and supports the inner side of the both side beams in the transverse direction as the U-shaped floor board unit is in contact with the both end flanges directly supported on the upper surface of the side beam. The drawbacks of the above invention: slab spans between main girders which are supported over abutments and deck width is less, which is not suitable for multilane Road/Rail and longer spans. The existing traffic is obstructed due to abutments supporting main girders and elaborate formwork arrangement.
Another prior art KR101476290 discloses a steel composite PSC corrugated steel plate U girder comprising: a lower flange (10) comprising a concrete layer (12) and a number of PS steel materials (11) provided inside the concrete layer (12) in a longitudinal direction; a pair of composite parts (20) connected respectively to both sides of the lower flange (10) such that the pair of composite parts are provided at an upper distance larger than a lower distance in distance between composite parts; and a pair of upper flanges (30) formed from concrete and connected respectively to upper sides of the pair of composite parts (20), in which the composite parts (20) comprises corrugated steel plates (24), lower coupling members (22) configured to couple lower portions of the corrugated steel plates (24) to the concrete (12) of the lower flange (10), and upper coupling members (26) configured to couple upper portions of the corrugated steel plates (24) to the concretes of the upper flanges (30). The corrugated plates of the above invention form web independent pair of composite parts and which is not suitable for wider/multi-lane Road/Railway bridges.
Yet another prior art KR100881921 “Opening steel composite U girder construction method” discloses a trapezoidal shaped opening type steel girder with high strength concrete in upper flange positive moment region and negative moment region with partial pre stressing.
From the above description, it is understood that the previous construction methods were being observed, which is not suitable for multilane road/rail and traffic obstructed. Two girders are adequate in place of multi girder to take loads and forces. U shaped RCC girder with steel girder bridges are being constructed with cross girder arrangement at the bottom level. There is a need for a construction of composite U shaped reinforced concrete and steel girders bridge deck by a way of providing a new force transfer system with composite interaction of U shaped RCC girder, main girder and cross girders resulting in substantial reduction of deflection and moments at center of span in main/cross girders making it suitable for longer spans.